Add a .hadolint config file

This is for the Dockerfile linter program `hadolint`.

Author: mhucka

.hadolint.yaml

@@ -0,0 +1,27 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+# Hadolint (a Dockerfile linter) used in this project's CI checks.
+# Info about options can be found at https://github.com/hadolint/hadolint/.
+# Rule/error numbers are described at https://github.com/hadolint/hadolint/wiki
+# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+format: tty
+no-color: false
+no-fail: false
+failure-threshold: error
+ignored:
+  # Multiple consecutive RUN stmts are usually deliberate. Don't flag that.
+  - DL3059